Hip dislocation

Dislocation of the hip can occur in the prosthetic hip (acquired) after replacement or in the native hip as part of polytrauma or low force injuries. Acquired hip dislocation has the highest incidence rate immediately after hip replacement surgery and continues to have a high incidence throughout the first three months following the surgery.

Congenital hip dislocation and its sequelae occurs throughout life and is covered in paediatric resources.

Classification

Simple and complex

• Simple – Pure dislocation without associated fracture
• Complex – Dislocation associated with fracture of acetabulum or proximal femur

Anatomic classification

Posterior dislocation (90%)

• Occurs with:
  • axial load on femur, typically with hip flexed and adducted
  • axial load through flexed knee (dashboard injury).
• Position of hip determines associated acetabular injury.
  • Increasing flexion and adduction favours simple dislocation.
• Associated with:
  • osteonecrosis
  • posterior wall acetabular fracture
  • femoral head fractures
  • sciatic nerve injuries
  • ipsilateral knee injuries (up to 25%).

Anterior dislocation

• Associated with femoral head impaction or chondral injury.
• Occurs with the hip in abduction and external rotation.
• Inferior versus superior.
• Hip extension results in a superior (pubic) dislocation.
• Flexion results in inferior (obturator) dislocation.

Presentation

Posterior hip dislocations are the most common type encountered in the emergency department. The affected limb will be shortened and internally rotated in this case.

Posterior dislocations with an associated fracture are categorised by the Thompson and Epstein classification system:

1. With or without a minor fracture
2. With a fracture of the posterior acetabular rim
3. With comminution of the acetabular rim
4. With a fracture of the acetabular floor
5. With a fracture of the femoral head

In an anterior dislocation the limb will not be shortened as noticeably and will be externally rotated.

In both cases, the affected leg is virtually immovable by the patient, and is usually extremely painful.

Imaging

Plain films can establish the diagnosis, but CT scans may be required after reduction of the native hip to assess for associated injuries.

Management options

If there are no other significant medical or surgical issues, isolated anterior or posterior hip dislocations should be managed within 6 hours using emergent closed reduction. This is contraindicated if there are fractures present.

Relocation is performed with the patient supine. Apply traction in line with deformity regardless of direction of dislocation, that is adducted internally rotated with posterior dislocation, and varying positions usually not internally rotated with anterior dislocations.

There must be adequate sedation and muscular relaxation to perform reduction. Hip stability should be assessed after reduction.

A post reduction CT scan is required to rule out femoral head fractures, intra-articular loose bodies and/or incarcerated fragments and acetabular fractures.

Prosthetic hips should be reduced in the same way. Post reduction, patients should have a pillow placed between the legs to maintain a neutral position and avoid hip adduction, particularly when the patient is waking from sedation and there may be reduced pain and control of movement.

Referral and follow up requirements

In most cases, a referral to orthopaedics and a hospital admission is required. Pending clearance from the orthopaedic team, some patients with prosthetic hips may be suitable for discharge post reduction.

Potential complications

Osteonecrosis can occur with native hip dislocation.

The staging system for osteonecrosis is:

1. Normal appearance of the femoral head. Patient is symptomatic (A technetium-99 bone scan may be used to confirm the diagnosis).
2. Femoral cysts, sclerotic changes, or both.
3. Crescent sign of subchondral collapse of the femoral head.
4. Joint space narrowing with acetabular cysts, osteophytes and cartilage damage.

Patient fact sheet

Prosthetic hip dislocation fact sheet

Further resources

• Professional articles: hip dislocations
  Source: Patient (UK)
• Hip dislocation
  Source: Orthobullets